<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <script>
        let age = +prompt("请输入你的年龄")
        alert('据我估计，五年之后，你会是' + (age + 5) + '岁')
        let num = +prompt("请输入一个数字")
        for (let i = 1; i <= num; i++) {
            sum += i
        }
        console.log('从1加到' + num + '的和为' + sum)
    </script>
</body>

</html>